Method for hardening treatment of aluminum or aluminum-base alloy

ABSTRACT

ON IMPLATATION OF POSITIVE IONS WITH THE CONCENTRATION OF ABOUT 10**14-10**16 /CM.2 COMPRISED OF AT LEAST ONE OF THE POSITIVE IONS B+, NE+. N+, P+, O+ OR AR+ INTO A PURE ALUMINUM FILM HAVING A KNOOP HARDNESS OF ABOUT 12, UNDER THE IMPLATATION ENERGY ON ORDER OF 45 KEY., THE SURFACE LAYER EXISTING IN THE DEPTH OF SEVERAL THOUSANDS A. FROM THE TREATED SURFACE OF THE ALUMINUM FILM EXHIBITS A KNOOP HARDNESS OF HK=16 TO 18 BY MEANS OF RADIATION DAMAGE. FURTHER, ON APPLYING HEAT TREATMENT WITH TEMPERATURES OF ABOUT 50 TO ABOUT 450*C. TO THE ABOVEMENTIONED INO-IMPLANTED PART, THE SURFACE HARDNESS OF THIS PART IS INCREASED.

April 23, 1974 MASAHIRO KlTADA ETAL 3,806,380

METHOD FOR HARDENING TREATMENT OF ALUMINUM OR ALUMINUM BASE ALLOY Filed March i972 3 Sheets-Sheet 2 FIG. 4

KNOOP HARDNESS (HK) HEAT TREATMENT TEMP. ("0) F IG, 6

a ANNEALED AT ROOM TEMPERATURE ANNEALED 2O L1, I

0 10' no lo lo 10' 10' N IMPLANTED CONC. (cm' April 23, 1974 MASAHIRO Kl ETAL 3,806,380

METHOD FOR HARDENING TREATMENT OF ALUMINUM 0R ALUMINUM-BASE ALLOY Filed March 6, 1972 5 Sheets-Sheet 3 United States Patent O US. Cl. 148-459 Claims ABSTRACT OF THE DISCLOSURE On implantation of positive ions with the concentration of about IO mm. comprised of at least one of the positive ions B+, Ne+, N' P 0+ or Ar+ into a pure aluminum film having a knoop hardness of about 13, under the implantation energy on order of 45 kev., the surface layer existing in the depth of several thousands A. from the treated surface of the aluminum film exhibits a knoop hardness of H =16 to 18 by means of radiation damage. Further, on applying heat treatment with temperatures of about 50 to about 450 C. to the abovementioned ion-implanted part, the surface hardness of this part is increased.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a method for the hardening treatment of the surface of aluminum or an aluminumbase alloy, and in particular to a method for the surfacehardening treatment for hardening a fine, specific part of a thin film of aluminum or an aluminum alloy.

Description of the prior art Pure aluminum is commonly very soft and also its mechanical strength is rather small. Therefore, in those cases where hardness or mechanical strength of some extent are required for such aluminum, alloying elements such as Mg, Cu, or Zn are added to the aluminum, so as to form a precipitation hardenable alloy of the aluminum. However, this method, wherein the whole material is hardened, has a remarkable disadvantage in the case of the requirement for increasing the hardness or strength of a complicated-shaped structural article or only a part of a deposited film or fine wire.

Recently there have been developed elements of microelectronic circuit parts with very fine and complicated structures, such as an integrated circuit (IC) or a large scale integrated circuit (LSI), etc., and good workable aluminum often is utilized to provide current terminals or leads for these elements. In this case, at the time of bonding between current terminals and leads, the comparable mild or soft nature of the pure aluminum is important from the aspect of the easiness of the bonding.

However, after the bonding of the above-mentioned terminals and leads, the mechanical strength of their bonding portion becomes a problem and also it is necessary to raise the hardness of the bonded portion. Besides, there are now many applications when the hardening of only the specific portion of the surface layer is required. For example, such hardening may be required for the purpose of applying anti-abrasion characteristic to various parts composed of aluminum, for the abrasive contact portion of the fine contact material, and for hardening only the portion where the heat strain concentrates, or for raising the strength of the thin films and fine wires.

However, heretofore a method has not yet been known for hardening a fine portion or the precisely limited sur- 3,806,380 Patented Apr. 23, 1974 ice face portion of a specific shape formed of aluminum or its alloy, and for effectively raising the mechanical strength thereof.

Generally, it is well known that when metal materials are exposed to the radiation of neutrons, radiation of electrons, or implantation of ions of various elements, the implanted ions or electrons collide with atoms at the crystal lattice point and that those atoms exhibit so-called radiation damage. Consequently, lattice defects such as dislocation, and vacancy, are introduced into the metal crystal, and the hardening of the metal material is elfected. However, heretofore many problems, such as the kind of ions that may be implanted in order to effectively obtain the hardened layer, or how much ions may be implanted for the energy applied to the ions when they are implanted, had not yet been resolved.

SUMMARY OF THE INVENTION One object of the present invention is to provide a method suitable for the hardening treatment of aluminum or an aluminum-base alloy which meets the before-mentioned requirements.

Another object of this invention is to provide a method for raising selectively the mechanical strength of aluminum or an aluminum-base alloy, particularly a fine, desired portion thereof.

A further object of this invention is to provide a method for forming a chemical compound layer composed of aluminum and any one of the elements: nitrogen, phosphorus, oxygen, and boron, on a desired fine portion of a material constituted of aluminum or an aluminum-base alloy.

Yet another object of this invention is to provide a heat treatment method for further raising the mechanical strength of the ion-implanted aluminum alloy.

The present method is substantially characterized by implanting a number of positive ions of at least one nuclide of boron, nitrogen, oxygen, phosphorus, neon, and argon, e.g., B+, N 0+, P+, Ne+ and Ar which are accelerated to the velocity higher than a predetermined velocity, onto the desired surface of aluminum or aluminum-base alloy.

In other words, on collision of this group of ions, as above-mentioned, accelerated to the velocity higher than the predetermined velocity with the desired surface of the aluminum or aluminum-base alloy, the ions are implanted into the material of aluminum or aluminum-base alloy within a depth of a few to several thousands A. from the surface of the aluminum or aluminum-base alloy, and then a number of lattice defects are introduced into this portion of the surface so as to increase the hardness and strength of this portion.

The hardness of pure aluminum is about 13 in knoop hardness, H; (with utilizing a diamond pressing unit; load 5 gr.: pressed for 30 seconds). According to an embodiment of this invention, it is possible to easily raise the aluminum hardness to the extent of about 16 to about 18 in knoop hardness H by means of implanting at least one of the above-mentioned ions with a certain concentration under a certain energy of ion-implantation.

Also, in the present invention after ion-implantation of ions such as those mentioned above, the ion-implanted portion is subjected to a heat treatment with a temperature of about 50-450 C. for 5 minutes to 2 hours. In this manner the hardening layer having the higher hardness may be obtained by effecting not only hardening by simple radiation damage, but also precipitation hardening at the alloying phase of the implanted ions and the aluminum.

Further, in the present invention, each ion of F 0 P+, N+ has reactivity for the metallic aluminum, and by means of heating that portion where the ions are implanted for comparatively short time of a few seconds to some dozen minutes, e.g., from about 5 to 30 seconds to about 48 minutes, within the range of the temperature on the order of about 450 to about 700 C. it is possible to form covering layers constituted of compounds of each of the above-mentioned ions and aluminum, namely, AlB A1 AlP or AlN, or to form the eutectic layers of these compounds and aluminum.

BRIEF DESCRIPTION OF THE DRAWING Other objects, features and advantages of the invention will become more apparent from the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a graph showing the relation between the quantity of implanted ions for the aluminum substrate and the surface hardness in accordance with this invention;

FIG. 2 is another graph showing the relation between the acceleration voltage of ions and the surface hardness;

FIG. 3 is also a graph showing the relation between the heat-treatment temperature and the surface hardness of the aluminum substrate on which ions are implanted;

FIG. 4 is a graph showing the relation between the heat-treatment temperature and the surface hardness of the aluminum substrate on which N+ ions are implanted;

FIG. 5 is an electron micrograph showing the eutectic phase of the aluminum and AlB obtained by an embodiment of the present invention;

FIG. 6 is a graph showing the relation between the quantity of the implanted ions and the surface hardness when N+ ions are implanted for the Al-Cu alloy substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the relation between the surface hardness and the concentration of various implanted ions at the time when the ions B+, N+, Ne- P+, 0+, and A+ with implanting energy of 45 kev., are respectively, implanted under the room temperature onto the aluminum plate on which an annealing treatment at about 400 C. for 1 hour has been effected.

According to the results shown, it will be apparent that the annealed pure aluminum has knoop hardness of about 13, and when the above-mentioned ions are implanted to the aluminum, in respective ions, with the increase of ionimplanting concentration, the hardness also increases and with an implanting concentration of more than about 10 /cm. regardless of the kind of implanted ions, the surface hardness may be the knoop hardness of H of more than about 16.

FIG. 2 shows a relation between the ion-implanting energy and the surface hardness of aluminum, upon implanting ions at a concentration of about 10 /cm. respectively, under room temperature, onto the aluminum plate which is annealed (in a manner similar to the embodiment of FIG. 1). It will be seen that, Ar+ ions have presented the largest effect of raising the hardness in the embodiment of FIG. 1, and N+ ions have presented the middle effect and B+ ions have presented the smallest effect thereon.

As a result, it is noted that in the present invention, the surface hardness can be influenced by not only the kind of nucleus of the ions and the implanting concentration but also the ion-implanting energy.

Herein, the hardness of aluminum after having been annealed is, generally in order of 13 in knoop hardness. For the preparation of electrodes as in micro-electronic circuit parts as previously mentioned, if a hardness of about 1.3 to about 1.5 times the hardness of pure aluminum could sufliciently be obtained, a particularly practical advantge would be achieved.

The following Table 1 shows the concentration of implanted ions the ion-implanting energy required for raising the surface hardness of the pure aluminum up to the TABLE 1 Implanting energy Nucleus kind Concentration lo /cm. and more.

* Kev. and more.

FIG. 3 shows the relation between the heat treating temperature and the hardness upon heat-treating the ionimplanted portions for about an hour, after having implanted P+, 0+, and B+ ions respectively of 10 cm. on aluminum annealed at about 400 C. for 1 hour, under an implanting energy of about 30 kev.

From this figure it is noted that as for the different nucleus kinds or types the hardness can be initially raised more, by effecting the predetermined heat treatment on the ion-implanted portion.

It is considered that the increase of the hardness owing to such heat treatment is due to a chemical reaction taking place mainly between the implanted ions and the aluminum, some chemical compounds such as All, A1 0 or AlB are precipitated in the aluminum phase thereby effecting a so-called precipitation hardening.

This heat treatment is effected under an atmosphere where the surface of the article of aluminum or aluminum alloy is not oxidized improperly. Also, the time for the heat-treatment is longer than the incubation time as to the hardening. In the case of this invention, the incubation time is for about 5 minutes in case of a heat treatment effected at the comparatively high temperature of about 400 C. or more and is for about 10 minutes in case of a heat treatment effected at the comparatively low temperature of about 50 to about C.

Also, it is desirable that the heat treatment may be effected within two hours since over two hours, the diffusion excessively proceeds so that the hardness would be lowered.

FIG. 4 is similar to the embodiment of FIG. 3, shows the relation of the heat-treatment temperatures and the surface hardness of the implanted portion, at the time of implanting the N+ ions to the annealed material surface of the pure aluminum with the rate of l0 /cm. under the implanting energy of 45 kev., and after giving a heattretment for one hour to said implanted portion. In other words, in. the case of N+ ions, differing from the case of other ions mentioned before, there is a tendency to lower the hardness of the ion-implanted portion due to the heat treatment and so an increased efiiciency due to the heattreatment cannot be expected.

FIG. 5 shows an electron micrograph of an ion-implanted portion at the time of implanting ions at a concentration of about 10 /cm. under the implanting energy of 45 kev. to the pure aluminum (subjected to an annealing treatment at 400 C. for about 1 hour) and then subjected to a heat treatment for the very short time (1-2 minutes) at about 560 to about 700 C.; a rapid cooling of said ion-implanted portion then being effected. In this micrograph, the phase shaped by the dark stripes represents the AlB phase and the matrix represents the aluminum phase.

As a result, it clearly noted that when the portion of the aluminum-base material, in which B+ ions are implanted, is heated instantaneously up to a comparatively high temperature, the eutectic phase of AIB and Al can be produced. The hardness of such eutectic phase portion is about 30 in knoop hardness.

Herein, in this method, the depth where the ions are implanted is in the range of several thousands A, Le, up to about 8,000 A. depending on the ions employed and the implanting energy, from the surface when the implanting energy to 'be given to the ions is in the range of order of about to about 100 kev. Minimum implanting energy is about 5 kev., whereas the absolute maximum has not yet been determined. Ion-implanting apparatus suitable for purposes of the invention are conventional and known to have capacities of 1,000 kev.

Generally the ions implanted into aluminum substrates are distributed in gauss distribution with half width of 500 to 1,000 A. Argon ions reach 400 to 500 A. and 1,500 to 3,000 A. in maximum depth when implantation energy is at about 10 kev. and 100 kev., respectively; whereas nitrogen ions with 1,200 A. and 8,000 A. when energy is at 10 kev. and 100 kev., respectively.

Therefore, by means of implanting the ions of an element having a chemical reactivity with aluminum by the stoichiometric concentration corresponding to the quantity of aluminum with thickness of a few to several thousand A., and giving thereto the suitable heat-treatment, it can easily be realized to form a compound layer of those elements and aluminum.

The elements which have such reactivity are (in this invention) B, O, P, and N. That is, it has clearly been shown by means of the electron diffraction test, that, when implanting these ions at concentrations of 10 "-10 /cm. and more on the surface of aluminum and then heating the ion-implanted portion for a relatively very short time (several secondssome dozen minutes) to about 450 to about 700 C., films of AlB A1 0 AlP, or AlN are formed.

Further, the surface hardness H, of the portion where the above-mentioned compound layer is produced is in the range of from about 40 to about 50.

In the method for measuring the knoop hardness shown in the embodiments of this invention, at the time of measuring, a diamond pressing unit is forced to the depth of a few ,u. exceeding the depth of a few to several thousands A. where the ions are implanted. Therefore, it will be recognized that it is rather difiicult to know the precise hardness of the ion-implanted portion, but it is believed that the hardness of this portion is more than a few times the measured valve.

FIG. 6 shows the relation between the concentration of implanted ions and the surface hardness at the time of implanting N+ ions to the A1-4% Cu alloy obtained by the annealing treatment at about 475 C. for about 1 hour, under the implanting energy of 45 kev. In this case, the surface hardness H of said alloy in the article at normal room temperature is equal to 28. Therefore, according to this embodiment, it is clear that the aluminum alloy may be submitted to the function of an increase of hardness owing to ion-implantation, more strongly than in the case of pure aluminum. This is probably because the alloyed aluminum has a large increase in hardness owing to the breeding diffusion and the precipitation hardening. Such effect is, of course, similarly caused also in the case of ions of other elements than N+ ions.

As described above, according to this invention, it is possible to harden the desired microportion and to increase the mechanical strength thereof, with the very simple and safe means, without necessitating any smelting working and the like, and further, this invention exhibits a large industrial potential when applied to various fields, including production of micro-electronic circuit apparatus such as IC and LSI, hardening of fine wires, hardening of micro-contact materials or application of anti abrasivity to the micro position, etc.

It will be appreciated that this invention is particularly suitable for the hardening of aluminum vapor deposited 6 films. The knoop hardness, H of such films is on the order of 13, which is comparable to hardness of annealed aluminum ingot. However, the present invention is applicable to work hardened aluminum substrate having a knoop hardness usually less than 20, e.g., 10 to 15.

Further, it will also be appreciated that the aluminumbase alloys are those alloys containing a major proportion of aluminum such as about or more.

While the novel principles of the invention have been described, it will be understood that various omissions, modifications and changes in these principles may be made by one skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. A method for hardening the surface of an aluminum or aluminum-base alloy article which comprises the steps of ion-implanting a number of positive ions of at least one nuclide selected from the group consisting of boron, and phosphorus onto the desired surface of said article at a concentration of at least about 10* /cm. under the energy of ion-implantation of not less than about 30 kev., and thereafter heating the ion-implanted portion at a temperature range of from about 50 to about 750 C. for a time sufficient to effect hardening of said portion.

2. The method of claim 1, wherein the concentration of said ions used is from about 10 to about IO /cm 3. The method according to claim 1, wherein said temperature is about 50 to about 450 C. and the heating time is about 5 minutes to about 2 hours to promote precipitation hardening thereof.

4. The method according to claim 1, wherein said temperature is about 450 to about 750 C. and the heating time is a period of time sufficient to produce a compound of said implanted ions and aluminum, on said surface, the formation of said compound increasing the hardness of said surface.

5. The method according to claim 1, wherein said article consists essentially of aluminum.

6. The method of claim 1, wherein ions implanted into said surface are distributed in gauss distribution with half width of 500 to 1000 A.

7. The method of claim 1, wherein the ions implanted into said surface have a thickness of a few to several thousands A.

8. The method of claim 1, wherein the energy of ion-implantation ranges up to kev. or more and concentration of said ions ranges from 10 10' /cm.

9. The method of claim 1, wherein said ion-implanted portion of said surface has a knoop hardness greater than pure aluminum.

10. The method of claim 9, wherein said surface has a knoop hardness of from about 16 to about 18.

11. The method according to claim 1, wherein phosphorus ions are implanted onto said desired surface.

12. The method according to claim 3, wherein phosphorus ions are implanted on said desired surface.

13. The method of claim 4, wherein phosphorus ions are implanted onto said desired surface.

14. A method for hardening of the surface of an aluminum or aluminum-base alloy article according to the claim 1, wherein the B+ ions are implanted onto the desired surface of said article at an implanting concentration of at least about 10 /cm. under the energy of ionimplantation of not less than about 40 kev.

15. A method for hardening of the surface of an aluminum or aluminum-base alloy article according to the claim 1, wherein the P+ ions are implanted onto the desired surface of said article at an implanting concentration of at least about 5 10 /cm.

16. The method of claim 1, wherein the aluminum base alloys are those alloys containing 90% or more aluminum.

(References on following page) 7 8 References Cited 2,902,583 9/ 1959 Steigerwald 219-50 UNITED STATES PATENTS 3,615,881 10/1971 Greene 148-4 9 9 7 Ehlers 250 49 5 TEX CHARLES N. LOVELL, Primary Examiner 9/1970 Kawakatsu 75-135 X 5 5/1957 Imich 75-133 X US 11/1959 Damask 250-49.5 11793.3; 204177, 192; 250-49.5 T 

